In modern multiple access systems, alternate and TX noise floor interferences generated by adjacent Terminal Stations (TS's) is one of the most significant factors in utilizing the system capacity and in affecting session quality. One common way to overcome this problem is to reduce the transmit power for each user so that the interference is eliminated or at least limited. However, it is obvious that the transmit power cannot be simply reduced without taking into considerations other factors such as that the reduced power should still be enough in order to maintain the required performances for a satisfactory traffic quality.
Two approaches are known in the art for carrying out adaptation of the Terminal Station (TS) transmission power when it is about to start transmitting to a Target Base Station (TBS). The first approach is by carrying out a process of pre-association with the target BS before starting the actual transmission process (while maintaining or temporary suspending the communication to SBS). By this approach, the TS would receive information about the link characteristics and/or power setup requirements by connecting to the TBS, and consequently will be able to modify its own power level accordingly. Following the pre-association period, the information is used by the TS to adjust its Tx power level when connecting to the TBS. The main disadvantage of such a method is the increase in the time required for the TS scanning process, causing significant adverse impact (interruption) on the TS active data traffic session with a Serving Base Station during scanning interval. The second approach is by using close loop power control during the preliminary stage of the communication with the TBS. By this approach, the TS sets its initial TX power for transmitting to the TBS according to predefined knowledge of the TBS requirements and/or measurements of transmission(s) received from the TBS. The main disadvantage of this approach is significant delay increase during a handover (HO), a process when a connection has to be transferred from one sector to another while the user moves between cells, during active data traffic session.
US 20030203742 describes wireless devices incorporated in an ad-hoc wireless network which adaptively set their transmission power levels based on locally available information. Initially, each such wireless device sets its transmission power level to a relatively low level, and gradually increases its power level up to a predetermined maximum transmission power level. As the transmission power increases, the wireless device is able to incrementally connect with additional wireless devices located at increasing distances from the wireless device. As the wireless device connects with these additional wireless devices, it checks a connectivity constraint. When the connectivity constraint is satisfied, the wireless device stops increasing its power and operates at its current power level.
US 20050147074 describes a method for autonomously optimizing the transmission power of an endpoint in a wireless network. The method includes monitoring the signal quality associated with data transfers between an access point in the wireless network and the endpoint at a certain transmission power and a certain transmission speed, checking whether the signal quality is acceptable and then adjusting the transmission power or the transmission speed based on whether the signal quality is acceptable.
US 20010012766 discloses a wireless communication apparatus that includes a variable power amplifier and a power amplifier. A variable power amplifier control unit controls the gain of the variable power amplifier for controlling the transmission power. Simultaneously therewith, a detection unit detects changes in conditions of the station and based upon the detected condition changes, a transmission power control bit controlling unit and a transmission power control period controlling unit change the control period of the transmission power control bit and the transmission power control range respectively, and the transmission power control bit is inserted into the transmission signal in be received by the other end of the link receiver.
In addition, one of the processes characterizing a mobile wireless network is a handover (HO) process in which a connection, currently existing between a device and a second device, needs to be transferred to another device during an active communication session. Such as in the case where a user moves from one cell to another cell while surfing the web, or in the midst of a phone call.
The problem with such a handover process is that it should be carried while the TS moves to an area serviced by a second BS and should communicate at the correct transmission power level, i.e. not too low and not too high. Otherwise, if it's transmission power is too low, it will not be received immediately at its first attempt and the handover process might take too long time, while on the other hand, if its transmission power is too high it might cause severe interference to other TSs that are already communicating with the second (target) BS. US 20050159176 describes a radio communication system where an associated-dedicated physical channel used for carrying out a soft hand-over and a high speed-dedicated physical control channel used for carrying out a hard hand-over, are combined.
Still, none of the prior art methods described provide an adequate solution to the problem of carrying out a reliable hand-over process which will be completed within a short enough time interval and will not consume too much resources of the wireless network.